Why has my phone suddenly changed to swipe unlock when all the settings still say pattern?

A

AC Question

I set the pattern unlock type the day I got my Samsung Galaxy J5, and it's been fine for a week. Today, it's suddenly changed to a swipe unlock (no security at all) but every setting says it's still set to pattern. I've even tried setting it again. I can't work out how to make it go back to pattern unlocks!